Elastomer materials integrated with high mechanical strength and excellent self-healing ability can be used as substrates in electronic skins, soft robots, and electrical devices. However, simultaneously enhancing the mechanical and self-healing properties of elastomers is still a great challenge because the self-healing ability of polymer materials is usually antagonistic to its mechanical strength. Herein, a novel healable polyurethane elastomer was developed using a double-network (DN) structure system. In the DN system, a loosely cross-linked chemical network was obtained via a photo-curable acrylic double bond, acting as a robust molecular framework and maintaining the elasticity of the polymer. Simultaneously, the physical cross-linked network produced by quadruple H-bonds of ureidopyrimidinone (UPy) units can not only achieve rapid reformation after fracture but also dissipate strain energy as a weak dynamic bond, endowing the elastomer with excellent self-healing ability and high stretchability. Owing to the accurate design, the synthesized elastomer exhibits excellent properties, including high tensile stress (13.71 MPa), high stretchability (∼500%), exceptional resilience and self-healing ability (90%). The robust healable elastomer enables the easy fabrication of composite conductors, which the prominent performance suggests as a great potential of the healable flexible sensor in next-generation wearable stretchable electronic devices, soft robots, and strain sensors.

A novel UV-curable hyperbranched polyurethane acrylate (FHBPUA) with excellent flexibility is successfully synthesized based on a reaction of hydroxyl terminated hyperbranched polyurethane (regarded as core) with flexible semiadduct urethane monoacrylate (regarded as arms). The structure and property of FHBPUA is firstly analyzed and then utilized as functional additives to ameliorate the UV-curing and mechanical properties of epoxy acrylate resin. The degree of branching of FHBPUA turns out to be 0.82. Its thermal decomposition process consists of three different stages, and the glass transition temperature is around 65 °C. The freestanding FHBPUA film (~30 μm thickness) can be UV-cured within 3 s, and its flexibility is up to 1 mm. With the increase of FHBPUA content to 10 wt %, the UV-curing time of UV1000 film decreases from 6 to 3 s, flexibility strikingly increases from 10 to 1 mm, and adhesive force also improves from 5 to 3 grades, meanwhile its glossiness is not influenced by FHBPUA. In addition, a certain amount of FHBPUA can improve the tensile strength and elongation at break of UV1000 film. This novel FHBPUA can be used not only to develop flexible UV-curable freestanding films but also as functional additives to perfect other UV-curable compositions like coatings, inks and 3D printed parts.